Vulcanized fluoroacrylate polymers



-Patented Oct. 29, 1957 VULCANIZED FLUOROACRYLATE POLYMERS Application December 2 1, 1953, I Serial No. 399,575 I 4 Claims. (Cl. 26t 41) N Drawing.

This invention relates to new and useful vulcanized fluoroacrylate polymers. 1 V

It provides rubbery vulcanized polymers that are stable even at elevated temperatures (up to at least 175 C.), are strong and snappy, have good low-temperature flexibility, have excellent resistance to oxidation by air, pure oxygen and ozone, have excellent resistance to fuming nitric acid, and have excellent resistance to hydrocarbon fuels, to aliphatic and aromatic oils, to ester type syn thetic hydraulic fluids and lubricants, and to common organic solvents. These vulcanized polymers can be used to provide nonfiammable coatings, liners and gaskets having exceptional utility for applications Where various'of the above-mentioned properties are of critical importance. Molded, extruded and cast articles of varied and useful shapes can be manufactured.

I have discovered that these objectives can be attained by vulcanizing with polyfunctional polyamine curing agents the polymers of normal 3-perfluoroalkoxy-1,1-dihydroperfluoropropyl acrylate ester monomers which contain 3 to 6 fully fluotinated carbon atoms in the molecule. Theseiester monomers can be represented by the following' formulas, the second being in abbreviated form:

wheren has an integer value of 1 to 4 and is the number of carbon atoms in the terminal perfluoroalkoxy group.

These esters and their polymers are described more fully' and are claimed in the companion application of F. A. Bovey and 'I F. Abere, S. N. 399,568, filed of even date herewith, and since abandoned in favor of the continuation in-part application, S. N. 640,348, filed Feb. 15, 1-957.

"The polyfunctional polyamine curing agents are organic compounds containing two or more primary or secondary amino groups. A preferred example is triethylene tetramine.

This class of vulcanizing agents was previously known tothe polymer art and had been used for vulcanizing conventional acrylate polymers, such as polymers of methyl acrylate and ethyl acrylate; monomers of ordinary organic chemistry in which the 'alkyl group is not fiuowhich includes an elaborate description of polymers of certain'highly 'fiuorinated acrylate'esters, and a variety of-vulca'riization techniques, but contains no mention of 2 using ainine curing agents for vulcanizing either the homopolymers or the heteropolymers.

I have discovered not only that these amine curing agents can vulcanize the above-mentioned fluoroacrylate polymers which I employ, but that vulcanized products can be obtained which are superior in their combination of desirable properties to those prepared by using any other vulcanization technique known to me. In particular, bymeans of my vulcanization procedure there can beobtained vulcanized homopolymers having the best flexibility at low temperatures that is obtainable in combination with a high degree of resistance to fuels, oils, solvents, and ester type synthetic hydraulic fluids and lubricants; In other words, the importance of my discovery does not reside in the mere fact of having found out that these fluoroacrylate polymers can be vulcanized with amine curing agents, but in having discovered that vulcanized'products of superior utility can be made. Vulcanizedrubbery compositions can be made which are without precedent and are superior for certain critical 1 usages to all previously known rubbery or elastomeric i is then'jwashed with'water and dried. Theh'omopolymers of the methoxy and ethoxy esters have good snappy elastic properties. Theh'ornopolymers'of the propoxy and butoxy esters are somewhat inferior in rubbery properties, al

though much improved by vulcanizationl Bulk and solu- C tion polymerization procedures can' also be employed to make rubbery polymers. Mercaptanor other chain trans fer agents can be employed to obtain polymersof lower average molecular weight, including liquid polymers. Thethan the heteropolymers.

latter can be vulcanized to obtain rubbery materials.

solid rubbery or non- Useful heteropolymers can be made by copolymeri zation of these perfluoroalkoxy ester monomers with other polymerizable monomers containing an ethylenic linkage. Examples of such co-monomers are butadiene, styrene,

acrylonitrile, isoprene, vinyl ethers, acrylates, methacry-. lates, and halogenated derivatives of such monomers, such i as perfluorobutadiene and fluoroprene. Use can be made as comonomers of the 1,1-dihydroperfluoroalkyl acr ylate esters which do not contain an ether oxygen atom,

Heteropolyniers employed in practicing the present invention should contain at least- 50 mol percent of the perfluoroalkoxy acrylate component. Homopo1yrners' of the perfluoroalkoxy acrylates (which contain substantially 10Q%' of this monomeric component) can be employed as. already indicated and are 'The presently preferred products ofthis inv'ention'are generally more de'sirable the homopo-lymers'of themethoxy and ethoxy'acrylate estersyvulcanized with a .polyfunctional amine. curing agent to obtain rubbery products havingthe'niaximum resistanceto nitric acid and to fuels, oils, solvents hydraulic fluids; combined with goodflow-te'mperat'u're' flexibility. w

Maximum strength is obtainedby compoundin polymer and vulcanizing agent with a substantial proper-. 15, V

tionof a reinforcing pigment '(suchas carbon black a small proportion of sulfur, which prevents premature cross-linking during processing andextends the useful service life at elevated temperatures, and a small proportron of a higher fatty acid (such as stearic acid), which aids inthe processing and also catalyzes the cross-linking;

reaction. These are optional ingredients. The presence of metal oxides shouldbe avoided since they interfere seriously-with the cure.

A- preferredamine curing agent is triethylene tetramine Thisaliphatic compound contains. two primary. and-two secondary. amino groups, linked: in. a chainbythree" thylene groups, and isa member. of the. class of unsubsti tuted golyalkylenepolyamine compounds. Asis understood 1nthe polymer art, there. isa widevariety ofpolyfunctional; polyamine compounds available as curing agents, the requirement being. that they. contain. at-least two amino groups of the primary; or. secondary.(but -not tert ary) types toprovide a plurality of functional amino groups. that produce cross-linking between the polymer of the appropriate side group alcohol and by formation of dior higher amides. The following are further examples of preferred polyamine curing agents that I have tested. tetraethylene pentamine, hexamyethylene diamine, propylene diamine, 1,3-diamino butane, hydroxyethyl ethylene diamine, aminoethyl ethanolamine, and trimene basef; the latter being a reaction product of ethyl chlo ride, formaldehyde and ammonia, sold by. Naugatuck Chemical Division of U. S. Rubber Co. The curing ggyents are generally employed in a proportion of 0.5 to

Compounding of the rubbery polymer can be carried out on conventional rubber mills. tained with the rolls maintained at about 50 to 65 C. 1 20 to 150 F No initial breakdown is required, as the rubber bands almost immediately. It tends to split and band around both rolls, but can be stripped readily. The compounding agents are preferably milledin the ,followingorder; (1) stearic acid or other processingaid, (2) carbon black ortother reinforcing pigment, (3) sulfur, 4) polyamine curing agent, added slowly in order to maintain a good rolling bank. The mastication period,

should be kept as short as consistent with obtaining thorough dispersion of. ingredients, Mastc fbatching.

techniques are possible and are usually beneficial.

Curing temperaturesfromabout 140 to 17 0 C. (280 to 340 F.) are suitable with conventional platenpressures, using a curing period of about one hour. Considerably shorter curing periods can be used by increasing the amount of curing agent or by increasing the temperature, orboth. In ordertQimproVecertain propertiea'particularly compression set, it is advantageous to heat the piece in an air oven after molding; 24 to 48 hour temperingat 150 C. (300 F.) has been found satisfactory. The use of a reinforcing pigment is essential to obtain rubbery products of adequate tensile strength and elasticity for most purposes. The most satisfactory carbon blacksare non-acidic furnace blacks, used in the proportionof, about 20 to 50 parts by weight per 100 parts of therubberypolymer. The best results have thus far been obtainedby using about 35 parts of HAF carbon black (high abrasion furnace black), acommercial example of whichis Philblack 0 (sold byPhillips Chemical Co.),'

which has an average particle diameter of about 45.n illi- 'micronsand a pH of 8.6; Examples, of inorganicrein V 'forcingpigments are: precipitated calcium carbonate, prea.

Best milling is ch:

Parts by weight Polymer 100 100 Stearic acid l 1 RAE carbon black Phllblack 0) (High abrasion furnace black) 35 35 Sulfur l i 1 Triethylene tetraniine l 1. 75

Using a rubbery methoxy homopolymer in the above formulas, samples were made up by mixing the ingredients on a rubber mill at C. and vulcanizing strips in a press for one hour at 150 C. vulcanization in each casetransfo'rmed the polymer from a thermoplastic material to a strong and elastic rubber, but product (B) was not as strong or elastic as product (A). The vulcanized polymers had the following properties:

Sample strips were immersed in White fuming nitric acidfor one week at 25 C. and swelled only, 30-40%. They showed no sign of deterioration and remained strong and. rubbery. Arsample strip of vulcanized polymer (B),was heated in air for 100 hours at 177 C. and showed only a 35% loss of strength and no change in ultimate elongation. Another sample was immersed in adioctyl sebacate type of synthetic lubricant for 100 hours at 177 C.; no

swelling occurred, loss of strength was only 18%, and" there was. no changein elongation. Another sample was immersedin boilingwater forhours; itswelled 47% but was not otherwise attacked.

In the abovetable the T10? values are the Gehman values obtained by measuring the torsional modulus at 25 C. in a Gehman apparatus, and then measuringthe modulus at reduced temperatures to determine the tempera.- ture at which the modulus is ten times the value for 25 C. The lower the T10 value the better the low-tempera,

ture flexibility.

A copolymer of the methoxy acrylate monomer and butadiene, the monomer ratio of the copolymer being 59:41 (mol ratio),-was compounded according to For mula A given above. These strips were vulcanized in a press for one'hour at 150 C. and had thefollowing properties:

a (c T10 C.) -39 Brittle point C.) ....L. 43 Percent swell after 48 hours at 25 C. in:

lso-octaneztoluene (70:30) 39 Benzene 42 Acetone 79 Ethyl acetate A comparison of the above data on the butadiene copolymer with that for the homopolymer, shows that-the butadiene, somewhat improved low ternperature flexibilitybut at a, sacrifice of resistance to swelling hydrocarbons and solvents. For most uses; the small gain in lowtemperature flexibility does not provide sufiicient compensation for the marked decrease in other properties.

In a further experiment using a homopolymer of the methoxy acrylate from a different batch, compounded as in Formula A above but with omission of the stearic acid, test strips vulcanized in a press for one hour at 150 C. were found to have the following properties:

Using the same compounding formula but substituting 2.0 parts of trimene base as the curing agent, and vulcanizing for one hour at 150 C., test strips were found to have closely similar properties, the tensile strength being 1020 p. s. i. and the ultimate elongation being 420%.

Preparation of polymers and monomers Emulsion polymerization in an aqueous vehicle to obtain a latex dispersion is the generally prefer-red procedure for making the fluoroacrylate homopolymers and heteropolymers employed in the present invention. The

following are typical emulsion recipes:

Parts by weight Ester monomer 100 100 Water (deoxygenated) 180 180 Duponol ME (sodium lauryl sulfate) 3 3 Borax 2 Naaszon 1 K2810: 0. 5

The reaction vessel is charged with the aqueous phase, the air is flushed out with nitrogen, and then the ester monomer is added. The vessel is sealed and the mixture is heated at a temperature of about 50 C. and stirred or agitated for about 2 /2 to 6 hours, the higher esters requiring longer reaction times. The resultant latex is stable and can be stored. It can be used as such; for instance, as an impregnating, coating or casting composi tion.

The latex can be diluted and frozen to coagulate the rubbery polymer, which is then washed with water and dried at 50 C. for 24 hours, resulting in a dried polymer mass that is tacky and will stick to a glass container.

A similar emulsion polymerization procedure can be employed for making heteropolymers. Thus copolymers of the alkoxy type monomers with corresponding perfluoro acrylate ester monomers that do not contain an ether-oxygen atom (cf. U. S. Patent 2,642,416), can be made by using the above recipes but with a mixture of the comonomers. Copolymers with butadiene can be made in a similar way by charging butadiene to the vessel, the total monomer charge being figured as 100 parts in following the recipe. In this case reaction times vary from 3 to 24 hours at 50 C. For best results, conversions should not be carried beyond 65-70%. An anti-oxidant, such as phenyl beta-naphthylamine, should preferably be added, either to the latex or by milling it into the dried copolymer mass.

Measured physical properties of the methoxy, ethoxy, propoxy and butoxy species of normal 3-perfluoroalkoxy- 1,1-dihydroperfluorpropyl acrylate esters, all of which are liquid at normal temperatures, are given in the following table, which lists the vacuum boiling points at the specified pressures, and the refractive indices and densities at 20 C.

Formula B. P. C.) an 114 CHzZCHCOOCHzGsFrOCF: 54 (50 mm.) 1.328 1.421 OHfiGHGOOOH202F4OC2F5 52 (30 mm) 1.320 1.460 CHrtCHCOOOHzCrF4OC3F7 44 (9 mm) 1.319 1.511 CH22CHOOOOH2C2F4OC4F9 48 (5 mm 1.319 1. 557

Formula B. P. 111. (14

CFaOC1F4CHzOH 98 1. 289 1. 595 C F 0C F OHrOH. 106 1. 287 1. 600 C3F7OC2F4CH2OH 1. 289 1. 650 C4F9OC2F4CH1OH 136 1. 292 1. 698

These alcohols can be prepared by the lithium aluminum hydride reduction of the methyl esters of the normal perfluoro(beta-alkoxypropionic) acids:

LiAlH4 F (0 Fr) 00 F 0 F20 O 0 CH F (CF2) HOOFZC F2OH20E The perfluoro(beta-alkoxypropionic) acids used for making the methyl esters can be readily prepared by hydrolysis of the corresponding sodium or potassium salts, by adding the salt to concentrated sulfuric acid and distilling off the perfluoro acid. The salts can be readily prepared by hydrolyzing the corresponding acid fluorides in aqueous NaOH or KOH solution. The perfluoro(betaalkoxypropionyl) fluorides, F(CF2)nOCF2CF2COF, can be obtained in useful yields from the corresponding hydrocarbon beta-alkoxypropionyl fluorides and chlorides by dissolving the latter in anhydrous hydrogen fluoride and electrolyzing the solution in a nickel-anode, iron-cathode cell at 0 to 20 C. and atmospheric pressure, the applied cell voltage being approximately 5 to 6 volts. Depending on the volatility of the particular acid fluoride product and the operating conditions, it will evolve with the cell gases or will settle to the bottom of the cell, and can be recovered by fractional distillation.

The preparation of the above fluoroacrylate esters and polymers, and the corresponding alcohols, is described in more detail in the previously-mentioned companion application of F. A. Bovey and I. F. Abere, S. N. 399,568 (since abandoned in favor of S. N. 640,348, filed Feb. 15, 1957); and the preparation of the ancillary methyl esters and acids in the companion application of T. I. Brice, W. H. Pearlson and H. M. Scholberg, S. N. 399,574; both filed of even date herewith. The latter application has since issued as Patent No. 2,713,593 (July 19, 1955).

I claim:

1. A vulcanized polymer product resulting from heating at vulcanization temperature a mixture comprising a polyfunctional aliphatic polyamine curing agent and a polymer containing at least 50 mol percent of polymerized normal 3-perfluoroalkoxy-1,1-diphydroperfluoropropyl acrylate component having the monomeric formula:

CH2 CHCOOCHzCFzCFzO CFz) 1F where n has an integer value of 1 to 4.

2. A rubbery vulcanized polymer product resulting from heating at vulcanization temperature a mixture comprising a polyfunctional aliphatic polyamine curing agent, a reinforcing pigment, and a rubbery polymer containing at least 50 mol percent polymerized normal 3-perflu0roalkoxy-l,l-dihydroperfluoropropyl acrylate component having the monomeric formula:

where n has an integer value of l to 4.

3. A rubbery vulcanized polymer product resultin from heating at vulcanization temperature a mixture comprising a polyfunctional aliphatic polyamine curing agent,

a carbon black reinforcing pigment, and a rubbery homopolymer of -Fkperfluoromethoxy-1,1-dihydroperfiuoropropyl acrylate.

4. A rubbery vulcanized polymer product resulting from heating at vulcanization temperature a mixture comprising a polyfunctional aliphatic 'polyamine curing agent, a carbon black reinforcing pigment, and a rubbery homopolymer of 3-perfluoroethoxy-1,l-dihydroperfluoropropyl acrylate.

No references cited. 

3. A RUBBERY VULCANIZED POLYMER PRODUCT RESULTING FROM HEATING AT VULCANIZATION TEMPERATURE A MIXTURE COMPRISING A POLYFUNCTIONAL ALIPHATIC POLYAMINE CURING AGENT, A CARBON BLACK REINFORCING PIGMENT, AND A RUBBERY HOMOPOLYMER OF 3-PERFLUOROMETHOXY-1,1-DIHYDROPERFLUOROPROPYL ACRYLATE. 